Effect of high-temperature drying of recycled paper on heat transfer rates and sheet properties

Abstract

A gas-fired paper dryer (GFPD) was evaluated in pilot- and full-scale environments. A corresponding study was done on the effect of high temperature on paper drying rates and paper properties. The process variables studied include temperature, moisture level, refining, and basis weight. In an ideal location, heat transfer rates are maximized with a minimum effect on sheet properties. Sheet curl is a function of recycling, refining, basis weight, and drying temperatures and can be minimized by correct placement of the GFPD. Results of this study indicate optimal installation location. The heat transfer coefficient is independent of the shell temperature in the constant rate drying zone and in the first following rate zone, but decreases with an increase in shell temperature in the second following rate zone. If a gas-fired dryer is located in either the constant rate zone or in the first following rate zone, the overall drying rate increases by approximately two to four percent per single gas-fired cylinder. By using several gas-fired dryers, it is possible to increase the overall drying rate by as much as 20%.